In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium, to form characters and images. The ink-jet printing methods have been rapidly spread because of their various advantages such as easiness of full coloration, low costs, capability of using a plain paper as the recording medium, non-contact with printed images and characters, etc.
Among such printing methods, in view of enhancing the weather resistance and water resistance of printed images and characters, an ink-jet printing method utilizing an ink containing a pigment as the colorant has now come to dominate (for example, refer to Patent Documents 1 and 2).
The Patent Document 1 aims at providing a water-based ink capable of forming clear characters or images printed, exhibiting an excellent weather resistance and ensuring a good printing condition, and discloses such a water-based ink composed of a water dispersion containing a colorant, and vinyl polymer particles obtained by copolymerizing (i) a macromer having a polymerizable functional group, (ii) a polymerizable unsaturated monomer having a salt-forming group and (iii) a copolymerizable monomer, in which the macromer is a silicone macromer and/or a styrene-based macromer having a polymerizable functional group at one terminal end thereof.
The Patent Document 2 aims at providing a water-based ink composition capable of exhibiting excellent water resistance and rubbing resistance as well as high lighter fastness, and a water-based ink for ink-jet printing having an excellent printability, and discloses a water-based ink composition containing an aqueous medium, polymer particles A obtained by incorporating dyes or pigments into a water-insoluble polymer and/or a self-dispersible pigment, and polymer particles B.
Although the conventional inks have been improved in ink characteristics to some extent, these inks still fail to provide fully unsatisfactory inks.
Patent Document 1: JP 2001-254038A
Patent Document 2: JP 2001-329199A